Method and Structure for Controlling Magnetic Field Distributions in an ExB Wien Filter

An ExB Wien mass filter providing a method and structure for mechanically adjusting the magnetic field distributions at the mass filter entrance and exit end caps. The reluctance of the flux return path may be modified by configuring pluralities of magnetic shims within slots at the outer diameters of the entrance and exit end caps, and also by configuring pluralities of magnetic plug shims within circular flux dams surrounding the entrance and exit apertures. Advantages of purely mechanical adjustment for the magnetic fields of the present invention, compared with prior art electromagnet adjustment methods include greater reliability, simplicity, lower cost, and lack of power dissipation. The invention may employ either permanent magnets or electromagnets for generation of the mass-separation magnetic field.